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Figure 13-18. Transponder phraseology.
Color and T
ype of SignalAircraft on the GroundMovement of Vehicles,Equipment and PersonnelAircraft in FlightSteady greenFlashing greenSteady redFlashing redFlashing whiteAlternating red and greenCleared to cross,proceed or goNot applicableStopClear the taxiway/runwayReturn to starting point on airportExercise extreme caution!!!!Cleared for takeoffCleared for taxiStopTaxi clear of the runway in useReturn to starting pointon airportExercise extreme caution!!!!Cleared to landReturn for landing (to be followed by steady green at the proper time)Give way to other aircraft andcontinue circlingAirport unsafe, do not landNot applicableExercise extreme caution!!!!
Figure 13-17. Light gun signals.sequencing of VFR aircraft to the primary airport. Class B service provides approved separation of aircraft based on IFR, VFR, and/or weight, and sequencing of VFR arrivals to the primary airport(s).Wake Turbulence
All aircraft generate wake turbulence while in flight. This disturbance is caused by a pair of counter-rotating vortices trailing from the wingtips. The vortices from larger aircraft pose problems to encountering aircraft. The wake of these aircraft can impose rolling moments exceeding the roll-
at which a pilot locates traffic. This service is not intended to relieve the pilot of the responsibility to see and avoid other aircraft. [Figure 13-19]
In addition to basic radar service, terminal radar service area (TRSA) has been implemented at certain terminal locations. TRSAs are depicted on sectional aeronautical charts and listed in the A/FD. The purpose of this service is to provide separation between all participating VFR aircraft and all IFR aircraft operating within the TRSA. Class C service provides approved separation between IFR and VFR aircraft, and
13-16
Figure 13-20. Vortex generation.
TRACK
TRACKTraffic information would be issued to the pilot of aircraft “A” as 12 o’clock. The actual position of the traffic as seen by the pilot of aircraft “A” would be 1 o’clock. Traffic information issued to aircraft “B” would also be given as 12 o’clock, but in this case the pilot of “B” would see traffic at 10 o’clock.Wind
Figure 13-19. Traffic advisories.
control authority of the encountering aircraft. Also, the turbulence generated within the vortices can damage aircraft components and equipment if encountered at close range. For this reason, a pilot must envision the location of the vortex wake and adjust the flightpath accordingly.
During ground operations and during takeoff, jet engine blast (thrust stream turbulence) can cause damage and upset smaller aircraft at close range. For this reason, pilots of small aircraft should consider the effects of jet-engine blast and maintain adequate separation. Also, pilots of larger aircraft should consider the effects of their aircraft’s jet-engine blast on other aircraft and equipment on the ground.Vortex Generation
Lift is generated by the creation of a pressure differential over the wing surface. The lowest pressure occurs over the upper wing surface, and the highest pressure under the wing. This pressure differential triggers the rollup of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wingtips. After the rollup is completed, the wake consists of two counter rotating cylindrical vortices. Most of the energy is within a few feet of the center of each vortex, but pilots should avoid a region within about 100 feet of the vortex core. [Figure 13-20]
Vortex Strength
The strength of the vortex is governed by the weight, speed, and shape of the wing of the generating aircraft. The vortex characteristics of any given aircraft can also be changed by the extension of flaps or other wing configuration devices as well as by a change in speed. The greatest vortex strength occurs when the generating aircraft is heavy, clean, and slow.
Vortex Behavior
Trailing vortices have certain behavioral characteristics that can help a pilot visualize the wake location and take avoidance precautions.
Vortices are generated from the moment an aircraft leaves the ground (until it touches down), since trailing vortices are the byproduct of wing lift. [Figure 13-21] The vortex circulation is outward, upward, and around the wingtips when viewed from either ahead or behind the aircraft. Tests have shown that vortices remain spaced a bit less than a wingspan apart, drifting with the wind, at altitudes greater than a wingspan from the ground. Tests have also shown that the vortices sink at a rate of several hundred feet per minute, slowing their descent and diminishing in strength with time and distance behind the generating aircraft.
13-17
25
Wake endsWake beginsTouchdownRotation
Figure 13-21. Vortex behavior.
When the vortices of larger aircraft sink close to the ground (within 100 to 200 feet), they tend to move laterally over the ground at a speed of 2–3 knots. A crosswind decreases the lateral movement of the upwind vortex and increases the movement of the downwind vortex. A tailwind condition can move the vortices of the preceding aircraft forward into the touchdown zone.
　
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